Conventionally, a magneto-optical disk memory has been used as a rewritable magneto-optical recording medium in its practical application. Such magneto-optical disk memory has such a drawback in that when a recording bit diameter and an interval between the recording bits are smaller with respect to a diameter of the light beam from a semiconductor laser converged on the magneto-optical memory, reproducing characteristics deteriorate.
The described problem is caused by the following reason. As the adjoining recording bits also fall within the diameter of spot of the laser beam on the target recording bit, it is not possible to reproduce each recording bit separately.
In order to counteract the above-mentioned problem, Japanese Laid-Open Patent Publication No. 81717/1993 (Tokukaihei 5-81717) discloses a superresolution magneto-optical reproducing technique. More concretely, as shown in FIG. 22 (a) and FIG. 22(b), a recording bit 201 is formed along each track 203 on the substrate 200. In this state, a laser beam 205 is projected onto a reproducing layer 3'. Then, the reproducing layer 3' and the recording layer 4' show respective temperature distributions with respect to a light intensity distribution of the light beam 205. Here, the reproducing layer 3' has an in-plane magnetization at room temperature, while has a perpendicular magnetization in response to a temperature rise.
The polar Kerr effect used as reproducing means for the magneto-optical recording medium is obtained only from a perpendicular magnetization component of the reproducing layer 3' whereon the light beam 205 is projected. Therefore, a perpendicular magnetization is shown only in the irradiated area with the light beam 205, i.e., the central portion having a temperature rise in a spot 206 of the laser beam on the reproducing layer 3', thereby permitting the reproducing signal to be obtained from the reproducing layer 3'.
As a result, only the magnetization state in the recording bit 201 at the central portion of the laser beam spot 206 of the recording layer 4' is copied to the reproducing layer 3' by the exchange interaction. While other recording bits 202 of the reproducing layer 3' show the in-plane magnetization, thereby enabling only information on the recording bit 201 to be reproduced.
For the above-mentioned reason, even if the diameter of each recording bit 201, 202 or an interval between the recording bits 201 and 202 is made smaller than the diameter of the spot 206 of the laser beam, the recording bits 201 and 202 can be reproduced, thereby enabling information recorded at high density to be reproduced.
However, in the described conventional arrangement, a still improved recording density of respective recording bits 201 and 202 are restricted by the problem associated with the reproducing operation.
More specifically, the reproducing layer 3' of the described prior art document, in general, has properties such that a transition gradually occurs from in-plane magnetization to perpendicular magnetization as the temperature thereof is raised. Here, since the temperature of recording bit 202 adjoining to the recording bit 201 to be reproduced is also raised, the magnetization in the reproducing layer 3' in the adjoining recording bit 202 is arranged in an intermediate direction in a process of changing from the in-plane direction and the perpendicular magnetization, thereby having a component in the perpendicular magnetization direction.
For the described reason, when reproducing information recorded on the recording bit 201, a perpendicular magnetization component in the adjoining recording bit 202 is also reproduced, thereby presenting the problem that each recording bit 202 cannot be reproduced by completely separating a signal from the recording bit 201.
Therefore, there is a restriction for reducing the size of the recording bits 201 and 202 and the interval between the recording bits 201 and 202 associated with the reproducing operation, thereby presenting the problem that a still improved recording density cannot be achieved.